1. Field of the Invention
The present invention relates to a distance factor learning device, which computes a distance factor value based on a signal generated in accordance with the movement of a mobile body and on distance information concerning the movement distance of the mobile body, and also concerns a distance factor learning method, a distance factor learning program, a recording medium recording the program, a movement condition computing device, and a present position computing device.
2. Description of Related Art
Vehicle-installed navigation devices have been known since prior, and such a device is installed in a vehicle, which is mobile body, for detection of the vehicle's movement condition and determination of the vehicle's present position based on the vehicle's movement condition.
This vehicle-installed navigation device is equipped with a GPS receiver, a computing device, a map storage device, and a display device.
With this vehicle-installed navigation device, the abovementioned computing device generates distance information and traveling direction information on the vehicle based on sensor outputs output from a vehicle velocity sensor and a yaw rate sensor.
Also this vehicle-installed navigation device detects the relative movement distance and relative movement direction of the vehicle at each unit time based on the distance information and traveling direction information. The navigation device then computes the present position of the vehicle from position information obtained from the GPS receiver and position information obtained based on the relative movement distance and relative movement direction. Thereafter, the map information stored in the map storage device are read and the computed present position is overlapped onto and displayed along with the map information on the display device, the position of one's own vehicle is determined.
Here, the vehicle velocity sensor outputs a vehicle velocity pulse signal at time intervals proportional to the rotation speed, for example, of a transmission output shaft or a wheel. The relative movement distance of the vehicle is then determined by multiplying the number of vehicle velocity pulses, which is based on the vehicle velocity pulse signal output at the vehicle velocity sensor, by a predetermined distance factor value as shown below in [Equation 1].Relative movement distance=Number of vehicle velocity pulses×Distance factor value  [Equation 1]
This distance factor value is the movement distance per single pulse of the vehicle velocity pulse signal and is computed based on the amount of movement of the GPS position obtained by the GPS receiver and the number of vehicle velocity pulses.
However, when the outer diameter of a tire of the vehicle changes due to a change of the pneumatic pressure of the tire or exchange of the tire, etc., the movement distance per single pulse of the vehicle velocity pulse signal and the timing at which the vehicle velocity pulse signal is output will differ before and after the change of the tire outer diameter. The distance factor value therefore needed to be corrected as necessary.
Thus prior, an averaging process, etc., was applied constantly to the computed distance factor value to correct the distance factor value, and the variation of the distance factor value was converged gradually to accommodate for a change in the outer diameter of a tire.
However, with the prior-art correction of the distance factor value, much time was required for the distance factor value to converge after a change of the vehicle's tire outer diameter. Thus until the distance factor value converged, errors occurred in the distance factor value, and this prevented the computing of an accurate relative movement distance or relative movement velocity and thus prevented accurate positioning of one's own vehicle.